The trouble is if you need VPC peering then it requires a dedicated VPC, dedicated k8s, dedicated instances. Confluent currently only offers one instance size, so that dedicated offering can't be scaled down.
PrivateLink allows for shared VPC and hypothetically a shared k8s. So the cost structure can be better on the Confluent side. Of course scaling down instance types would make a huge difference, but I don't think that's supported currently. The cheaper option is multi-tenant Kafka clusters.
In general, I think VPC peering is a dead end for use cases where you are connecting two companies networks together. It's not great operationally and puts a lot of security / filtering burden on each party.
PrivateLink is a much better option.